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The influence of gonadal steroid hormones and social environment on sexually differentiated behavior patterns in wild and captive immature chimpanzees

THE INFLUENCE OF GONADAL STEROID HORMONES AND SOCIAL
ENVIRONMENT ON SEXUALLY DIFFERENTIATED BEHAVIOR PATTERNS IN
WILD AND CAPTIVE IMMATURE CHIMPANZEES
by
Angela Maria Garbin
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(INTEGRATIVE AND EVOLUTIONARY BIOLOGY)
May 2012
Copyright 2012 Angela Maria Garbin

Sex differences between males and females have been systematically documented for more than 150 years. However, the extent to which physiological and social factors influence these sex differences is still debatable (Arnold and Breedlove, 1985; Fitch and Denenberg, 1998; Wallen and Hassett, 2009). The goal of the present study was to gain insight into the influence gonadal steroid hormones and social environment have on the expression of sexually differentiated behaviors in male and female immature wild and captive chimpanzees. I performed a study on the wild Kanyawara community of chimpanzees located in Kibale National Park, Uganda over two 4-month field seasons. The age categories relevant to the present study were as follows: juveniles (3-7yrs); adolescents (8-15yrs). Based on these categories, subjects consisted of 3 juvenile and 7 adolescent females and 7 juvenile and 5-6 adolescent males. I contrasted the behavior of wild chimpanzees with that of captive chimpanzees located at The Los Angeles Zoo, Los Angeles over a six month period. Subjects were placed in the same age categories and consisted of 2 juvenile females, 1 juvenile male, 3 adolescent males and 1 adolescent female. Play, agonistic, affiliative and sexual behaviors were recorded. Non-invasive urine samples were also collected on all subjects and assayed for testosterone (T), estrogen (E1C) and progesterone (PdG) in males and females respectively. ❧ My results showed that both juvenile and adolescent males and females exhibited behavioral sex differences in both captivity and in the wild. Among wild juveniles, males engaged in higher frequencies of play and copulatory behavior compared to females. However, both male and female hormone levels remained relatively stable. Wild adolescent male mean T levels were significantly higher compared to wild juvenile males and they displayed significantly higher rates of aggression than juvenile males which were positively associated with high T levels. Wild adolescent females had significantly higher E1C levels compared to wild juvenile females and higher frequencies of copulations but this was not positively associated with high E1C levels. ❧ By comparing captive and wild populations, I found that captive juvenile males engaged in significantly more play and had significantly higher copulation rates than wild juvenile males. In addition, there was no significant difference between mean T levels in captive and wild juvenile males. Captive adolescent males had significantly higher rates of aggression and bluff displays compared to wild adolescent males. However, wild adolescent males had higher T levels than captive adolescent males. Wild adolescent females had significantly higher E1C levels compared to captive adolescent females. ❧ Based on these results I concluded that both juvenile and adolescent males and females exhibit behavioral sex differences in both captivity and in the wild. In juveniles, some of these differences can be attributed to the organizational effects of steroid hormones. However, others are clearly influenced by the social environment. The activation of steroid hormones experienced by adolescents had an obvious effect on sexually dimorphic behaviors observed in adolescent males and females. Therefore, the present study provided further support for the organizational and activational effects of gonadal steroid hormones but it also has shown that social environments have an active role in the expression of sexually differentiated behavioral patterns.

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THE INFLUENCE OF GONADAL STEROID HORMONES AND SOCIAL
ENVIRONMENT ON SEXUALLY DIFFERENTIATED BEHAVIOR PATTERNS IN
WILD AND CAPTIVE IMMATURE CHIMPANZEES
by
Angela Maria Garbin
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(INTEGRATIVE AND EVOLUTIONARY BIOLOGY)
May 2012
Copyright 2012 Angela Maria Garbin